Cyanine dye

ABSTRACT

The present invention provides organic dye compounds having their absorption maxima in a region ranging from the ultraviolet region to a relatively short wavelength visible region and uses thereof. The present invention provides specific monomethine cyanine dyes, light absorbents and optical recording media comprising the monomethine cyanine dyes, and a process for producing the monomethine cyanine dyes which comprises a step of reacting a quaternary ammonium salt of nitrogen atom-containing heterocyclic compound having a reactive methyl group with a quaternary ammonium salt of nitrogen atom-containing heterocyclic compound having an appropriate leaving group.

REFERENCE TO RELATED APPLICATIONS

The present application is the national stage under 35 U.S.C. 371 ofinternational application PCTJP00/08297, filed Nov. 24, 2000 whichdesignated the United States, and which international application wasnot published under PCT Article 21(2) in the English language.

FIELD OF THE INVENTION

The present invention relates to novel organic dye compounds, andparticularly to monomethine cyanine dyes which are sensitive to visiblelight of a relatively short wavelength.

BACKGROUND OF THE INVENTION

In a multimedia age, optical recording media such as compact discrecordable (CD-R, a write-once memory using compact disc); and digitalversatile disc (DVD-R, a write-once memory using digital video disc),have been highlighted. Optical recording media can be classified roughlyinto inorganic optical recording media which have recording layerscomposed of inorganic substances such as tellurium, selenium, rhodium,carbon, or carbon sulfide; and organic optical recording media whichhave recording layers composed of light absorbents containing organicdye compounds.

Among these optical recording media, organic media are usually preparedby dissolving a polymethine dye in an organic solvent such as2,2,3,3-tetrafluoro-1-propanol (abbreviated as ITFPII hereinafter),coating the solution onto the surface of a polycarbonate substrate,drying the solution to form a recording layer, and sequentiallyattaching closely a reflection layer made of a metal such as gold,silver or copper and a protective layer made of an ultraviolet rayhardening resin onto the surface of the recording layer. When comparedwith inorganic optical recording media, organic optical recording mediahave the drawback that their recording layers may be easily changed byexposure to light such as reading- and natural light, but have the meritthat they can be manufactured at a lower cost because their recordinglayers can be formed by preparing solutions of light absorbents anddirectly coating the solutions onto the surface of substrates. Also,organic optical recording media are now becoming the predominantlow-cost optical recording media because of the merits that they aremainly composed of organic substances so that they are substantiallyfree of corrosion even when contacted with moisture or sea water; andbecause information, which is stored in optical recording media in aprescribed format, can be read out using a commercialized reader usingthermal deformation type optical recording media, a kind of organicoptical recording media.

What is urgently required of organic optical recording media is toincrease their recording capacity to suit this multimedia age. Theresearch for such an increment now eagerly continued in this field is toshorten the wavelength of 635-650 nm now used as a writing light to awavelength of 450 nm or less to increase the recording capacity per oneside to a level from 4.7 giga bytes (GB) to 15 GB or higher. The opticalrecording media with such an increased capacity can record six hours ofmoving images in quality equivalent to standard TV and just record twohours of moving images in quality equivalent to high-quality TV.However, most of the organic dye compounds now used in optical recordingmedia are not applicable to laser beams with a wavelength of 450 nm orless, and therefore such organic dye compounds could not fulfill theneed for high storage density required in many fields.

SUMMARY OF THE INVENTION

In view of the foregoing, the object of the present invention is toprovide organic dye compounds which are sensitive to visible lighthaving a relatively short wavelength, and to provide uses thereof.

To attain the above object, the present inventors eagerly studied andscreened compounds. As a result, they found that specific monomethinecyanine dyes (may be called a “monomethine cyanine dyes” hereinafter),which are obtainable through a step of reacting a quaternary ammoniumsalt of a nitrogen atom-containing heterocyclic compound having anactive methyl group with a quaternary ammonium salt of a nitrogenatom-containing compound having a leaving group, have an absorptionmaximum in a relatively short-wavelength visible region, and whichsubstantially absorbs visible light in such a visible region. They alsofound that, among these monomethine cyanine dyes, those which havesensitivity to laser beams with a wavelength of 450 nm or less when in athin layer form can form minute pits on the recording surfaces at arelatively high density when irradiated by a laser beam at a wavelength450 nm or less. The present invention was made based on the creation ofthe novel monomethine organic dye compounds which are sensitive tovisible light having a relative short wavelength, and the discovery oftheir industrially useful characteristics.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows visible absorption spectra of one of the monomethinecyanine dyes of the present invention when in solution form and in thinlayer form.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the monomethine cyanine dyesrepresented by the Formula 1.

φ1-CH=φ2  Formula 1:

In Formula 1, φ1 and φ2 are the same or different heterocyclic groupsrepresented by any one of Formulae 2 to 8 as resonance structures.

Throughout Formulae 2 to 5, Z represents, for example, a mono orpolycyclic aromatic ring or heterocycle such as benzene, naphthalene,pyridine, quinoline, naphthylidine or quinoxaline ring, which may haveone or more substituents. Examples of such substituents are halogenssuch as fluorine, chlorine, bromine, and iodine; ether groups such asmethoxy, ethoxy, propoxy, isopropoxy, butoxy, tert-butoxy, pentyloxy,benzyloxy, phenoxy, o-tolyloxy, m-tolyloxy, and p-tolyloxy groups; estergroups such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl,phenoxycarbonyl, o-tolyloxycarbonyl, m-tolyloxycarbonyl,p-tolyloxycarbonyl, acetoxy, and benzoyloxy groups; aromatic hydrocarbongroups such as phenyl, o-tolyl, m-tolyl, p-tolyl, xylyl, mesityl,o-cumenyl, m-cumenyl, p-cumenyl, nitrophenyl, and biphenyl groups;alkylsulfonyl groups such as methylsulfonyl, ethylsulfonyl,propylsulfonyl, and butylsulfonyl groups; alkylamino sulfonyl groupssuch as methylaminosulfonyl, dipropylaminosulfonyl, ethylaminosulfonyl,diethylamino sulfonyl, propylaminosulfonyl, dipropylaminosulfonyl, andbutylaminosulfonyl groups; methylene dioxy group; nitro group; cyanogroup; sulfo group; and aliphatic hydrocarbon groups such as those whichhave 1 to 5 carbon atoms such as methyl, ethyl, propyl, isopropyl,isopropenyl, 1-propenyl, 2-propenyl, butyl, isobutyl, sec-butyl,tert-butyl, 1-butenyl, 1,3-butadienyl, pentyl, isopentyl, neopentyl, and2-pentenyl groups. When the substituents have hydrogen atoms, one ormore of the hydrogen atoms may be substituted, for example, withhalogens such as fluorine, chlorine, bromine, and iodine. In Formulae 2to 5, when Z does not exist, one or more of the substituents like thosein the above Z may be bound to the position of Z. In the case of usingthe monomethine cyanine dyes of the present invention in opticalrecording media which use laser beams with a wavelength of not longerthan 450 nm, and in the case of using different types of cyclic cores ofφ1 and φ2 into a non-symmetric structure as a whole molecular structureand of forming either or both of the cyclic cores into a condensed ring,such a condensed ring is preferably restricted to form a bicyclicstructure as a whole cyclic core structure, varying depending on that φ1and φ2 are which of Formulae 2 to 5.

Throughout Formulae 2 to 8, R₁ represents an aliphatic hydrocarbon groupand R₂ represents a hydrogen atom or the same or different aliphatichydrocarbon group as in R₁. These aliphatic hydrocarbon groups may haveone or more substituents. Examples of such aliphatic hydrocarbon groupsare those which have one to eight carbon atoms, usually, for example,methyl, ethyl, propyl, isopropyl, isopropenyl, 1-propenyl, 2-propenyl,2-propynyl, butyl, isobutyl, sec-butyl, tert-butyl, 2-butenyl,2-butynyl, 1,3-butadienyl, pentyl, isopentyl, neopentyl, tert-pentyl,1-methylpentyl, 2-methylpentyl, 2-pentenyl, 2-pentene-4-ynyl, hexyl,isohexyl, 5-methylhexyl, heptyl, and octyl groups. One or more of thehydrogen atoms of these aliphatic hydrocarbon groups may be substitutedwith halogens such as fluorine, chlorine, bromine, and iodine; ethergroups such as methoxy, trifluoromethoxy, ethoxy, propoxy, isopropoxy,butoxy, tert-butoxy, pentyloxy, benzyloxy, and phenoxy groups; estergroups such as methoxycarbonyl, trifluoromethoxycarbonyl,ethoxycarbonyl, propoxycarbonyl, acetoxy, trifluoroacetoxy, andbenzoyloxy groups; aliphatic hydrocarbon groups such as phenyl, o-tolyl,m-tolyl, p-tolyl, xylyl, mesityl, o-cumenyl, m-cumenyl, p-cumenyl,nitrophenyl, and biphenyl groups; heterocyclic groups such as 2-pyridyl,piperidino, pyrolidino, piperidinyl, morpholino, and 2-quinolyl groups;and others such as hydroxy, carboxy, sulfo, and sulfonic acid estergroups.

Throughout Formulae 2 to 8, X⁻ represents an appropriate anion, usually,one selected from inorganic acid anions such as fluoride, chloride,bromide, iodide fluoric acid, chloric acid, bromic acid, iodic acid,perchloric acid, phosphoric acid, phosphoric acid hexafluoride, antimonyacid hexafluoride, tin acid hexafluoride, fluoroboric acid, andtetrafluoroborate ions; organic acid anions such as thiocyanic acid,benzenesulfonic acid, naphthalenesulfonic acid, naphthalenedisulfonicacid, benzenecarboxylic acid, alkylcarboxylic acid, alkylsulfonic acid,trihaloalkylsulfonic acid, nicotinic acid ions, andtetracyanoquinonedimethane ions; and metal complex anions such as thoseof azo, bisphenyldithiol, thiocatecholchelate, thiobisphenolatechelate,bisdiol-α-diketone, and their related compounds. In Formulae 2 and 8, R₁or R₂ has a negatively charged substituent, and X³¹ does not exist whenthe substituent forms an internal salt.

The present invention relates to the monomethine cyanine dyes which havethe aforesaid structures and absorption maxima in a relatively shortwavelength visible region. Examples of the monomethine cyanine dyes are,for example, those represented by Chemical Formulae 1 to 48 which have avariety of uses in the fields which require compounds that absorb lightin such a visible region. The monomethine cyanine dyes have absorptionmaxima in a region ranging from an ultraviolet region to a relativelyshort wavelength visible region, usually, at wavelengths of 500 nm orless, more particularly, about 350-450 nm. In particular, among thesemonomethine cyanine dyes, those which are sensitive to laser beams withwavelengths of 450 nm or less when in a thin-layer form, preferably,those which substantially absorb such laser beams in longer wavelengthregions with their absorption maxima can be quite advantageously used asmaterials for high-density optical recording media such as DVD-Rs, whichuse laser beams with wavelengths of 450 nm or less as a reading light.

The monomethine cyanine dyes according to the present invention can beprepared by various methods. When production cost is important, themonomethine cyanine dyes can be advantageously prepared through a stepof reacting a quaternary ammonium salt of a nitrogen atom-containingheterocyclic compound having a reactive methyl group with a quaternaryammonium salt of nitrogen atom-containing heterocyclic compound havingan appropriate leaving group. According to this method, the monomethinecyanine dyes used in the present invention can be produced in asatisfactory yield by either reacting the compounds, represented byFormula 9 having φ1 corresponding to Formula 1, with the compoundsrepresented by Formula 10 having φ2 corresponding to Formula 1; orreacting the compounds, represented by Formula 11 having φ1corresponding to Formula 1, with the compounds represented by Formula 12having φ2 corresponding to Formula 1. In Formulae 10 and 11, Lrepresents an appropriate leaving group, usually, a mercapto group oralkylthio group such as methylthio, ethylthio, or propylthio group.

For example, adequate amounts (usually, about equimolar) of thecompounds represented by Formulae 9 and 10 or the compounds representedby Formula 11 and 12 are optionally dissolved in an appropriate solventand reacted by heat refluxing at ambient temperature or at a highertemperature under heating and stirring conditions, after being admixedwith an adequate amount of a basic compound(s) such as sodium hydroxide,sodium bicarbonate, potassium carbonate, sodium acetate, potassiumacetate, ammonia, tri-ethylamine, pyridine, piperidine, pyrrolidine,morpholine, 1,8-diazabicyclo [5.4.0]-7-undecene, aniline,N,N-dimethylaniline, or N-diethylaniline; an acid compound such ashydrochloric acid, sulfuric acid, nitric acid, methane sulfonic acid,p-toluenesulfonic acid, acetic acid, anhydrous acetic acid, anhydrouspropionic acid, trifluoroacetic acid, or trifluorosulfonic acid; or aLewis acid compound such as aluminum chloride, zinc chloride, tintetrachloride, or titanium tetrachloride.

Examples of the solvent include hydrocarbons such as pentane, hexane,cyclohexane, octane, benzene, toluene, and xylene; halogen compoundssuch as carbon tetrachloride, chloroform, 1,2-dichloroethane,1,2-dibromoethane, trichloroethylene, tetrachloroethylene,chlorobenzene, bromobenzene, and α-dichlorobenzene; alcohols and phenolssuch as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,isobutyl alcohol, isopentyl alcohol, cyclohexanol, ethylene glycol,propylene glycol, 2-methoxyethanol, 2-ethoxyethanol, phenol, benzylalcohol, cresol, diethylene glycol, triethylene glycol, glycerine;ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran,tetrahydropyran, 1,4-dioxane, anisole, 1,2-dimethoxyethane, diethyleneglycol dimethyl ether, dicyclohexyl-18-crown-6, methyl carbitol, andethylcarbitol; ketones such as furfural, acetone, ethyl methyl ketone,and cyclohexanone; acids and derivatives thereof such as acetic acid,anhydrous acetic acid, trichloroacetic acid, trifluoroacetic acid,anhydrous propionic acid, ethyl acetate, butyl carbonate, ethylenecarbonate, propylene carbonate, formamide, N-methyl formamide,N,N-dimethylformamide, N-acetamide, N,N-dimethylacetamide,hexamethylphosphoric triamide, and trimethyl phosphate; nitrites such asacetonitrile, propionitrile, succinonitrile, and benzonitrile; nitrocompounds such as nitromethane and nitrobenzene; sulfur-atom-containingcompounds such as dimethylsulfoxide and sulfolane; and water, which allcan be used in an appropriate combination, if necessary.

In the case of using such solvents, the greater the volume of solventsthe lower the reaction efficiency. On the contrary, the lower the volumeof solvents, the more difficult the homogenous heating and stirring,become and undesirable side-reactions may easily occur. Thus, thesolvents should preferably be used in an amount up to 100 times byweight of the material compounds, usually, in the range of 5-50 times.Depending on the types of the material compounds and the reactionconditions used, the reaction should preferably be terminated within 10hours, usually, within 0.5-5 hours. The reaction procedure can bemonitored by conventional methods such as thin-layer chromatography, gaschromatography, and high-performance liquid chromatography. Aftercompletion of the reaction, the intact reaction mixture, if necessary,can be subjected to conventional counter-ion exchange reaction to obtainthe monomethine cyanine dyes, having a desired counter ion, of thepresent invention. All the monomethine cyanine dyes represented byFormulae 1 to 48 can be easily obtained by the above methods. Everycompound represented by Formulae 9 to 12 can be obtained in accordancewith the conventional methods for preparing cyclic cores in the relatedcompounds.

The monomethine cyanine dyes thus obtained can be used in the form of anintact reaction mixture, however, prior to use, they are purified byconventional methods used for purifying the related compounds such asdissolution, extraction, separation, decantation, filtration,concentration, thin-layer chromatography, column chromatography, gaschromatography, high-performance liquid chromatography, distillation,crystallization, and sublimation. If necessary, these methods can beused in an appropriate combination. For use in optical recording mediasuch as DVD-Rs and dye lasers, the monomethine cyanine dyes of thepresent invention should preferably be purified by methods such asdistillation, crystallization and/or sublimation, prior to use.

The light absorbents referred to in the present invention include thosein general which contain one or more of the monomethine cyanine dyes,have sensitivity to visible light of a relatively short wavelengthinherent to the monomethine cyanine dyes, and use the properties tosubstantially absorb the relatively short-wavelength visible light,independently of the composition and the physicochemical properties ofthe light absorbents. Accordingly, the light absorbents of the presentinvention may be those which consist of the monomethine cyanine dyes andoptionally one or more other ingredients depending on use. One of thefields in which the light absorbents can be advantageously used is ofoptical recording media, and, in such a field, the light absorbents canbe preferably used as materials for composing recording layers fororganic optical recording media, particularly, high-density opticalrecording media which use laser beams with wavelengths of 450 =m or lessas a writing light. When used in optical recording media, the lightabsorbents can be used, if necessary, together with one or moreconventional materials used in optical recording media, for example,light absorbents containing other organic dye compounds sensitive tovisible light, light-resistant improvers, binders, dispersing agents,flame retardants, lubricants, antistatic agents, surfactants, thermointerference agents, plasticizers, colorants, developers, andsolubilizers.

The light absorbents of the present invention for use in organic opticalrecording media or organic ablation-type optical recording media can beprepared in accordance with the methods used for conventional opticalrecording media because they do not need any special treatment andhandling when used in optical recording media. For example, to controlthe reflectance and the absorptance in recording layers, the monomethinecyanine dyes can be, if necessary, incorporated with one or more otherorganic dye compounds sensitive to visible light and further one or moreconventionally used light-resistant improvers, binders, dispersingagents, flame retardants, lubricants, antistatic agents, surfactants,thermal interference agents, and plasticizers. The resulting mixturesare then dissolved in organic solvents, and the solutions arehomogeneously coated over either surface of substrates by spraying,soaking, roller coating, or rotary coating method; and dried to formthin layers as recording layers containing light absorbents, and, ifnecessary, followed by forming reflection layers to be closely attachedon the recording layers by means of vacuum deposition, chemical vapordeposition, sputtering, or ion-planting method using metals such asgold, silver, copper, platinum, aluminum, cobalt, tin, nickel, iron, andchromium or using commonly used materials for organic reflection layersto attain reflection efficiency, which makes it possible to readrecorded information, for example, of 20% or higher, preferably, 30% orhigher. Alternatively, to protect the recording layers from scratches,dust, stains, etc., coatings may be applied over the recording layerswith ultraviolet ray hardening resins or thermosetting resins whichcontain flame retardants, stabilizers or antistatic agents, and then thecoatings are hardened by irradiating light or heating to form protectivelayers attached closely over the reflection layers. Thereafter, ifnecessary, a pair of the above substrates with recording-, reflection-,and recording-layers are faced and attached together using, for example,adhesives or viscous sheets; or protective plates, which are made of thesame materials and shapes as the substrates, are attached to theprotective layers of the substrates.

Other organic dye compounds usable in combination with the monomethinecyanine dyes of the present invention are not specifically restricted aslong as they are sensitive to visible light and capable of controllingthe reflectance or the absorptance of recording layers of opticalrecording media when used with the monomethine cyanine dyes. Examples ofsuch organic dye compounds are polymethine dyes such as cyanine,merocyanine, oxonol, azulenium, squallilium, styryl, pyrylium,thiopyrylium, and phenanthrene dyes, which have either a monomethinechain that may have one or more substituents or a polymethine chain suchas di-, tri-, tetra-, penta-, hexa-, and hepta-methine-chains, whereinthe both ends of the monomethine chain or the polymethine chain bind thesame or different cyclic cores such as imidazoline, imidazole,benzimidazole, α-naphthoimidazole, β-naphthoimidazole, indole,isoindole, indolenine, isoindolenine, benzindolenine,pyridinoindolenine, oxazoline, oxazole, isoxazole, benzoxazole,pyridineoxazole, α-naphthoxazole, β-naphthoxazole, selenazoline,selenazole, benzoselenazole, α-naphthoselenazole, β-naphthoselenazole,thiazoline, thiazole, isothiazole, benzothiazole, α-naphthothiazole,β-naphthothiazole, tellulazoline, tellulazole, benzotellulazole,α-naphthotellulazole, β-naphthotellulazole, aquaridine, anthracene,isoquinoline, isopyrrole, imidaquinoxaline, indandione, indazole,indoline, oxadiazole, carbazole, xanthene, quinazoline, quinoxaline,quinoline, chroman, cyclohexanedione, cyclopentanedione, cinnoline,thiodiazole, thiooxazolidone, thiophene, thionaphthene, thiobarbituricacid, thiohydantoin, tetrazole, triazine, naphthalene, naphthyridine,piperazine, pyrazine, pyrazole, pyrazoline, pyrazolidine, pyrozolone,pyran, pyridine, pyridazine, pyrimidine, pyrylium, pyrrolidine,pyrroline, pyrrole, phenazine, phenanthridine, phenanthrene,phenanthroline, phthalazine, pteridine, furazan, furan, purine, benzene,benzoxazine, benzopyran, morpholine, and rhodanine rings, which may haveone or more substituents. In addition, the following organic dyecompounds can be exemplified; acridine, azaannulene, azo, azo metalcomplex, anthraquinone, indigo, indanthrene, oxazine, xanthene,dioxazine, thiazine, thioindigo, tetrapyraporphyradine,triphenylmethane, triphenothiazine, napthoquinone, pyromethene,phthalocyanine, benzoquinone, benzopyran, benzofuranone, porphyrin,rhodamine dyes, and their related compounds. Depending on use, the aboveorganic dye compounds can be used in an appropriate combination.Preferable organic dye compounds used in combination with themonomethine cyanine dyes of the present invention are those which haveabsorption maxima in a visible region, particularly, those atwavelengths of 400-850 nm, when in a thin-layer form. The organic dyecompounds as disclosed in Japanese Patent Application No. 343,211/99,titled “Styryl dyes” and Japanese Patent Application No. 355,176/99,titled “Optical absorbents and uses thereof”, both of which were appliedfor by the same applicant of the present invention, are most preferablyused.

The light-resistant improves used in the present invention are, forexample, nitroso compounds such as nitrosodiphenylamine, nitrosoaniline,nitrosophenol, and nitrosonaphthol; and metal complexes such as those ofdithiolate and formazan, for example, tetracyanoquinodimethanecompounds, diimmonium salts, “NKX-1199”(bis[2′-chloro-3-methoxy-4-(2-methoxyethoxy)dithiobenzyl]nickel)produced by Hayashibara Biochemical Laboratories, Inc., Okayama, Japan,which all can be used in an appropriate combination, if necessary.Preferable light-resistant improvers are those as disclosed in JapanesePatent Application No. 163,036/99, titled “Formazan metal complexes”applied for by the same applicant as the present invention, whichcontain metal complexes of dithiolate and formazan, most preferably,those which contain metal complexes of metals such as nickel, zinc,cobalt, iron, copper, palladium, etc., and as ligands one or more of theformazan derivatives and their tautomers, which have a pyridine ring atC-5 in the formazan skeleton and have a pyridine or furan ring bound toC-3 of the formazan skeleton. The combination use of the light-resistantimprovers lowers the solubility of the monomethine cyanine dyes of thepresent invention in organic solvents and effectively inhibits theundesirable deterioration, fading, color change, and quality change ofthe monomethine cyanine dyes, which are inducible by the exposure ofreading and environmental lights, without spoiling the preferableoptical properties of the monomethine cyanine dyes. As for thecomposition ratio, 0.01-5 moles, preferably, 0.1-1 mole of alight-resistant improver(s) can be incorporated into one mole of thepresent monomethine cyanine dye(s) while increasing or decreasing theratio. The light-resistant improvers should not necessarily existindependently of the monomethine cyanine dyes of the present invention,and if necessary, the monomethine cyanine dyes can be formulated intosalts, complexes, or compounds by combining with commonly used organicmetal complex anions, which are capable of improving the lightresistance, such as those of azo, bisphenyldithiol, phenylbisdiol,thiocatecholchelate, thiobisphenolatechelate, or bisdithiol-α-diketone,which are disclosed in Japanese Patent Kokai Nos. 19,355/89, 139,034/93,323,478/97, 6,651/98, etc., by using appropriate spacers andcrosslinking agents such as alkoxides or cyanates of metal elements, forexample, titanium, zirconium, aluminum, etc., or complexes of thesemetal elements having carbonyl compounds or hydroxy compounds asligands.

The monomethine cyanine dyes of the present invention have satisfactorysolubility in organic solvents without substantially causing problemsand do not substantially restrict the types of organic solvents used forcoating the light absorbents on substrates. Thus, in the preparation ofoptical recording media according to the present invention, for example,TFP used frequently to prepare optical recording media and the followingorganic solvents other than TFP can be selected and used in anappropriate combination: For example, hydrocarbons such as hexane,cyclohexane, methylcyclohexane, dimethylcyclohexane, ethylcyclohexane,isopropylcyclohexane, tert-butylcyclohexane, octane, cyclooctane,benzene, toluene, and xylene; halogenides such as carbon tetrachloride,chloroform, 1,2-dichloroethane, 1,2-dibromoethane, trichloroethylene,tetrachloroethylene, ychlorobenzene, bromobenzene, andα-dichlorobenzene; alcohols and phenols such as methanol, ethanol,propanol, isopropanol, 2,2,2-trifluoroethanol, butanol, 2-butanol,isobutanol, isopentanol, cyclohexanol, ethylene glycol, propyleneglycol, 2-methoxyethanol (methyl cellosolve), 2-ethoxyethanol (ethylcellosolve), phenol, benzyl alcohol, cresol, diethylene glycol,triethylene glycol, glycerine, and diacetone alcohol; ethers such asdiethyl ether, diisopropyl ether, tetrahydrofuran, tetrahydropyran,1,4-dioxane, anisole, 1,2-dimethoxyethane, cyclohexyl-18-crown-6, methylcarbitol, and ethylcarbitol; ketones such as furfural, acetone,1,3-diacetyl acetone, ethyl methyl ketone, and cyclohexanone; esterssuch as ethyl acetate, butyl acetate, ethylene carbonate, propylenecarbonate, and trimethyl phosphate; amides such as formamide, N-methylformamide, N,N-dimethylformamide, N-methylacetamide,N,N-dimethylacetamide, and hexamethylphosphoric triamide; nitriles suchas acetonitrile, propionitrile, succinonitrile, and benzonitrile; nitrocompounds such as nitromethane and nitrobenzene; amines such as ethylenediamine, pyridine, piperidine, morpholine, and N-methylpyrrolidone; andsulfer atom-containing compounds such as dimethylsulfoxide andsulfolane.

Particularly, since the monomethine cyanine dyes of the presentinvention have relatively high solubility in easily volatile organicsolvents such as TFP, methyl cellosolve, ethyl cellosolve, and diacetonealcohol, they are substantially free from dye crystallization whensequentially dissolved in the organic solvents, coated on substrates,and dried; and do not cause inconsistent thickness and surface of theformed recording layers. Most of the monomethine cyanine dyes of thepresent invention have satisfactory solubility in non-halogen solvents,for example, cellosolves such as methyl cellosolve and ethyl cellosolve;alcohols such as diacetone alcohol; and ketones such as ethyl methylketone and cyclohexanone. Accordingly, the above non-halogen solventshardly damage substrates or spoil the environment when used to dissolvethe present light absorbents for coating on substrates.

The substrates used in the present invention are not specificallyrestricted and usually processed by forming appropriate materials, forexample, into discs, 12 cm in diameter and 0.1-1.2 mm in thickness,using the methods such as compression molding, injection molding,compression-injection molding, photopolymerization method (2P method),thermosetting integral method, and lightsetting integral method.Depending on their final use, the discs thus obtained can be usedsingularly or plurally after appropriately attaching them together withadhesives or adhesive sheets, etc. In principal, any one of thematerials for the substrates can be used in the present invention aslong as they are substantially transparent and have a transmittance ofat least 80%, preferably, at least 90% at a wavelength ranging from 350nm to 800 nm. Examples of such materials are glasses, ceramics, andothers such as synthetic resins including polyacrylate, poly(methylmethacrylate), polycarbonate, polystyrene (styrene copolymer),polymethylpentene, polyester, polyolefin, polyimide, polyetherimide,polysulfone, polyethersulfone, polyarylate, polycarbonate/polystyrenealloy, polyestercarbonate, polyphthalatecarbonate,polycarbonateacrylate, non-crystalline polyolefin, methacrylatecopolymer, diallylcarbonatediethylene-glycol, epoxy resins, and phenolicresins, among which polycarbonate- and acrylic-resins are usually usedfrequently. In the case of using plastic substrates, concaves forexpressing synchronizing-signals and addresses of tracks and sectors areusually transferred to the internal circuit of the tracks during theirformation. The form of concaves are not specifically restricted andpreferably formed to give 0.3-0.8 μm in average wide and 50-150 nm inwidth.

Considering the viscosity, the light absorbents of the present inventionare prepared into 0.5-5% (w/w) solutions in the above organic solvents,and then uniformly coated over substrates to form a dried recordinglayer with 10-1,000 μm, preferably, 50-300 nm in thickness. Prior to thecoating of the solutions, preliminary layers can be formed over thesubstrates to protect them and improve the adhesion ability of thesubstrates, if necessary. Materials for the preliminary layers are, forexample, high molecular weight substances such as ionomer resins,polyamide resins, vinyl resins, natural resins, silicons, and liquidrubbers. In the case of using binders, the following polymers can beused alone or in combination in a weight ratio of 0.01-10 times of thelight absorbent(s): Cellulose esters such as nitrocellulose, cellulosephosphate, cellulose sulfate, cellulose acetate, cellulose propionate,cellulose lactate, cellulose palmitate, and celluloseacetate/propionate; cellulose ethers such as methyl cellulose, ethylcellulose, propyl cellulose, and butyl cellulose; vinyl resins such aspolystyrene, poly(vinyl chloride), poly(vinyl acetate), poly(vinylacetal), poly(vinyl butyral), poly(vinyl formal), poly(vinyl alcohol),and poly(vinyl pyrrolidone); copolymer resins such as styrene-butadienecopolymers, styrene-acrylonitrile copolymers,styrene-butadiene-acrylonitrile copolymers, vinyl chloride-vinyl acetatecopolymers, and maleic anhydride copolymers; acrylic resins such aspoly(methyl methacrylate), poly(methyl acrylate), polyacrylate,polymethacrylate, polyacrylamide, and polyacrylonitrile; polyesters suchas poly(ethylene terephthalate); and polyolefins such as polyethylene,chlorinated polyethylene, and polypropylene.

Explaining the method fobrusing the optical recording media according tothe present invention, the high-density optical recording media such asDVD-Rs according to the present invention can write information at arelatively high density by using laser beams with wavelengths of 450 nmor less, particularly, 350-450 nm irradiated by semiconductor laserssuch as those of InN, GaN, InGaN, InAlGaN, InGaNAs, BlnN, InGaNP, InP,GaP, GaAsP, and SiC, which oscillate in a blue or blue-violet region; orother laser beams, which oscillate in a red region, for example,distributed feed back lasers in which second harmonic generatingmechanisms are installed in AlGaAs semiconductor laser elements. To readinformation, laser beams are used which have wavelengths similar to orslightly shorter or longer than those used for writing information. Asfor the laser power for writing and reading information, in the opticalrecording media of the present invention, it is preferably set to arelatively high level which exceeds the threshold of the energy requiredfor forming pits when used for writing information, while it ispreferably set to a relatively low level, i.e., a level below thethreshold, when used for reading the recorded information, although thelaser power level varies depending on the types and ratios of otherlight-resistant improvers used in combination with the light absorbentsof the present invention: Generally, the laser power level can becontrolled by increasing or decreasing to a power level of over 5 mW,usually, 10-50 mW for writing; and to a power level of 5 mW or lower,usually, 0.1-5 mW for reading the recorded information. The recordedinformation is read out by detecting the changes of both the reflectionlight level and the transmission light level in the pits and thepit-less parts on the recorded surface of optical recording media.

Accordingly, in the optical recording media according to the presentinvention, quite minute pits with a pit width of below 0.5 μm/pit and atrack pitch of below 0.74 μm, which are below the levels of the existingDVD-Rs, can be formed smoothly at a relatively high density using alaser element with an oscillation wavelength of 450 nm or less. Forexample, in the case of using a substrate, 12 cm in diameter, one canprepare an extremely high density optical recording medium having arecording capacity far exceeding 4.7 GB per one side, i.e., a recordingcapacity for about two hours of information in the form of images andvoices in quality similar to that of high quality televisions, whichrecording capacity could not be easily attained by the existing DVD-Rs.

Since the optical recording media according to the present invention canrecord information in the form of characters, images, voices, and otherdigital information at a relatively high density, they areadvantageously useful as recording media for professional and family useto record/backup/keep documents, data, and computer software. Particularexamples of the kinds of industries and the forms of information, towhich the optical recording media of the present invention can beapplied, are as follows: Drawings of construction and engineering works,maps, ledgers of loads and rivers, aperture cards, architecturalsketches, documents of disaster protection, wiring diagrams, arrangementplans, information from newspapers and magazines, local information,reports of construction works, etc., which all relate to architectureand civil construction; blueprints, ingredient tables, prescriptions,product specifications, product price tables, parts lists, maintenanceinformation, case study files of accidents and problems, manuals forclaims, production schemes, technical documents, sketches, details,company house-made product files, technical reports, analysis reports,etc., which all relate to manufacturing; customer information,correspondents information, company information, contracts, informationfrom newspapers and magazines, business reports, reports of companycredibility, records of stocks, etc., which all relate to sales; companyinformation, records of stocks, statistical documents, information fromnewspapers and magazines, contracts, customer lists, documents ofapplication/notification/licenses/authorization, business reports, etc.,which all relate to finance; information regarding properties, sketchesof construction, maps, local information, information from newspapersand magazines, contracts of leases, company information, stock lists,traffic information, correspondents information, etc., which all relateto real property and transportations; diagrams of writings and pipingarrangements, documents of disaster protection, tables of operationmanuals, documents of investigations, technical reports, etc., which allrelate to electric and gas supplies; patient files, files of patientclinical histories and case studies, diagrams of medicalcare/institution relationships, etc., which all relate to medicalfields; texts, collections of questions, educational documents,statistical information, etc., which all relate to private andpreparatory schools; scientific papers, records in academic societies,monthly reports of research, research data, documentary records andindexes thereof, etc., which all relate to universities, colleges, andresearch institutes; inspection data, literatures, patent publications,weather maps, analytical records of data, customer files, etc., whichall relate to information; case studies on laws; membership lists,history notes, records of works/products, competition data, data ofmeetings/congresses, etc., which all relate toorganizations/associations; sightseeing information, trafficinformation, etc., which all relate to sightseeing; indexes of homemadepublications, information of newspapers and magazines, who's who files,sport records, telop files, scripts for broadcastings, etc., which allrelate to mass communications and publishing; and maps, ledgers of roadsand rivers, fingerprint files, resident cards, documents ofapplication/notification/license/authorization, statistical documents,public documents, etc., which all relate to government offices.Particularly, the write-once type optical recording media of the presentinvention can be advantageously useful for storing records of patientfiles and official documents, which must not be deleted or rewrittenintentionally, and also used as electronic libraries for art galleries,libraries, museums, broadcasting stations, etc.

As a rather specific use, the optical recording media of the presentinvention can be used to prepare and edit compact discs, digital videodiscs, laser discs, MDs (a mini disc as information recording systemusing photomagnetic disc), CDVs (a laser disc using compact disc), DATs(an information recording system using magnetic tape), CD-ROMs (aread-only memory using compact disc), DVD-ROMs (a read-only memory usingdigital video disc), DVD-RAMs (a writable and readable memory usingdigital video disc), digital photos, movies, video software, audiosoftware, computer graphics, publishing products, broadcasting programs,commercial messages, computer software, game software, etc.; and used asexternal program recording means for large-sized computers and carnavigation systems.

Hereinbefore, the use of the light absorbents of the present inventionin the field of optical recording media has been mainly explained withreference to their application examples to organic optical recordingmedia which use laser beams with wavelengths of 450 nm or less as awriting light. However, in the field of optical recording media, thelight absorbents of the present invention can be advantageously used notonly in high-density optical recording media but commonly used inoptical recording media such as CD-Rs and DVD-Rs as materials forcontrolling and calibrating the absorptance and the reflectance bycombining them with one or more other organic dye compounds which aresensitive to laser beams with wavelengths of 635-650 nm or 775-795 nm.Even in the case of using organic optical recording media which uselaser beams with wavelengths of 450 nm or less as a writing light, pitscan be indirectly formed, without directly forming pits on substratesusing the monomethine cyanine dyes of the present invention, bycombining with one or more other organic dye compounds sensitive to alonger wavelength light, for example, a laser beam with a wavelength of635-650 nm or 775-795 nm, in such a manner that an exited energy bylaser beams with wavelengths of 450 nm or less is transferred throughthe monomethine cyanine dyes to the organic dye compounds to decomposethe compounds. The term “optical recording media” as referred to in thepresent invention means those in general which use the characteristicfeatures of specific monomethine cyanine dyes that have absorptionmaxima in a relatively short-wavelength visible region and substantiallyabsorb such a visible light, and includes, in addition to the organicoptical recording media, for example, those prepared by the thermalcoloration method which uses the chemical reaction of coloring agentsand developers induced by the heat generated when the organic dyecompounds absorb light, and those prepared by the technique called“moth-eye type technique” which uses the phenomenon that the above heatsmoothes the pattern of periodical unevenness, provided on the surfaceof substrates.

The monomethine cyanine dyes of the preset invention have absorptionmaxima in a region ranging from an ultraviolet region to a relativelyshort wavelength visible region and substantially absorb light in such avisible region, and therefore in addition to being used in the aforesaidoptical recording media, they can be advantageously used as materialsfor polymerizing polymerizable compounds by exposure to visible light,light absorption materials for lithography, laser action substances indye lasers which oscillate in a blue or blue-violet region, and lightabsorbents for dying clothes. If necessary, in combination with one ormore other light absorbents capable of absorbing light in ultraviolet,visible and/or infrared regions, the light absorbents of the presentinvention can be used in clothes in general and other materialsincluding building/bedding/decorating products such as drapes, laces,casements, prints, venetian blinds, roll screens, shutters, shopcurtains, blankets, thick bedquilts including comforters, peripheralmaterials for thick bedquilts, covers for thick bedquilts, cottons forthick bedquilts, bed sheets, Japanese cushions, pillows, pillow covers,cushions, mats, carpets, sleeping bags, tents, interior finishes forcars, and window glasses including car window glasses; sanitary andhealth goods such as paper diapers, diaper covers, eyeglasses, monocles,and lorgnettes; internal base sheets/linings/materials for shoes;wrappers; materials for umbrellas; parasols; stuffed toys; lightingdevices; filters/panels/screens for information displaying devices suchas televisions and personal computers which use cathode-ray tubes,liquid crystal displays, electroluminescent displays, and plasmadisplays; sunglasses; sunroofs; sun visors; pet bottles; storage; vinylhouses; lawns; optical fibers; prepaid cards; and windows of ovensincluding electric ovens. When used for wrapping, injecting, andenclosing the above articles, the light absorbents of the presentinvention advantageously prevent living bodies and products fromproblems and discomforts induced by environmental lights such as naturaland artificial light or minimize the above problems and discomforts.Furthermore, they can advantageously regulate the color, tint, andappearance and adjust the light reflected from or passed through thearticles to a desired color balance.

The following examples describe the preferred embodiments according tothe present invention:

EXAMPLE 1 Monomethine Cyanine Dyes

Five grams of 3-ethyl-2-methylthiazolium iodide, six grams of3-methyl-2-methylthiobenzoxazolium methylsulfate, 2.5 ml oftriethylamine, and 25 ml of acetonitrile were placed in a reactionvessel, and the mixture was heat refluxed for two hours, followed byremoving the acetonitrile by distillation and washing the resultingresidues with ethyl ether and acetone. The crude crystal formed wascollected and recrystallized in ethanol to obtain 1.3 g of a yellowcrystal of the monomethine cyanine dye, represented by Chemical Formula4. Upon conventional measurement, the crystal had a melting point of199-200° C.

The monomethine cyanine dye with satisfactory optical properties thusobtained can be used in various fields as light absorbents includingoptical recording media.

EXAMPLE 2 Monomethine Cyanine Dye

Three grams of 2,3,4-trimethyloxazolium iodide, 2.4 g of3-ethyl-4-methyl-2-methylthiothiazolium iodide, 2 ml of triethylamine,and 20 ml of acetonitrile were placed in a reaction vessel, and themixture was heat refluxed for two hours. Thereafter, the reactionmixture was treated similarly as in Example 1 to obtain 0.8 g of ayellow crystal of the monomethine cyanine dye represented by ChemicalFormula 17. Upon conventional measurement, the crystal had a meltingpoint of 308° C.

The monomethine cyanine dye with satisfactory optical properties thusobtained can be used in various fields as light absorbents includingoptical recording media.

EXAMPLE 3 Monomethine Cyanine Dye

2.8 g of 3-methyl-2-methylthiobenzoxazolium methylsulfate, 3 g of1,2,3,3-tetramethylindolenium iodide, 24 ml of pyridine, and 1.2 ml ofacetic acid were placed in a reaction vessel, and the mixture was heatrefluxed for three hours. The solvents were removed from the reactionmixture, and the residue was admixed with 20 ml of methanol andsubjected to counter-ion exchange by the addition of 4.8 ml aqueoussolution containing 1.6 g potassium iodide. Thereafter, the crudecrystal formed was collected and recrystallized from methanol to obtain1.2 g of a yellow crystal of the monomethine cyanine dye represented byChemical Formula 36. Upon conventional measurement, the crystal had amelting point of 267-269° C.

The monomethine cyanine dye with satisfactory optical properties thusobtained can be used in various fields as light absorbents includingoptical recording media.

EXAMPLE 4 Monomethine Cyanine Dye

3.7 g of 3-methyl-2-methyl-5-phenylbenzoxazolium iodide, 2.9 g of3-ethyl-2-methylthiobenzoxazolium iodide, 2.2 ml of triethylamine, and20 ml of acetonitrile were placed in a reaction vessel, and the mixturewas heat refluxed for two hours. The reaction mixture was treatedsimilarly as in Example 1 to obtain 2.5 g of a yellow crystal of themonomethine cyanine dye represented by Chemical Formula 6. Uponconventional measurement, the crystal had a melting point of 280° C.

Although the production conditions and the yields of the monomethinecyanine dyes used in the present invention are somewhat varied dependingon their structures, they, including the compounds represented byFormulae 1 to 48, can be produced in a desired yield by the methods inExamples 1 to 4 which comprise a step of reacting a quaternary ammoniumsalt of nitrogen atom-containing heterocyclic compound having a reactivemethyl group with a quaternary ammonium salt of nitrogen atom-containingheterocyclic compound having an appropriate leaving group, or can beproduced in accordance with conventional methods.

EXAMPLE 5 Optical Properties of Monomethine Cyanine Dye

<Example 5-1: Light Absorption Properties of Monomethine Cyanine Dye>

The monomethine cyanine dyes in Table 1 were measured for their visibleabsorption spectra when dissolved in methanol and formed on glasssubstrates, respectively. The results are tabulated in Table 1, and thevisible absorption spectrum of the monomethine Icyanine dye representedby Chemical Formula 17 when in a liquid form and in a thin-layer formare shown in FIG. 1.

TABLE 1 Wavelength of absorption maximum (nm) Monomethine cyanine dyeSolution Thin layer Chemical Formula 4 350 351 Chemical Formula 6 380371 Chemical Formula 14 387 380 Chemical Formula 16 383 374 ChemicalFormula 17 379 375 Chemical Formula 36 396 440 Chemical Formula 38 341342

As evident from the results in Table 1 and FIG. 1, the monomethinecyanine dyes tested had absorption maxima in relatively short wavelengthvisible regions, particularly, at wavelengths of 450 nm or less both inthe forms of solution and thin layer. Most of these monomethine cyaninedyes had absorption maxima at wavelengths of 350-400 nm when in solutionand thin layer forms, and the ends of their absorption maxima in theirlonger wavelength regions extended up to about 450 nm when in a thinlayer form. The fact evidences that the light absorbents, comprising themonomethine cyanine dyes of the present invention, have sensitivity to arelatively short-wavelength visible light, and most of the lightabsorbents substantially absorb laser beams with wavelengths of 450 nmor less in their longer wavelength regions with their absorption maxima.

<Example 5-2: Light-resistance Improvement for Monomethine Cyanine dye>

Fifteen milligrams of either of the monomethine cyanine dyes in Table 2was added to three milliliters of TFP, and as a light-resistant improvertwo milligrams of the formazan nickel complex represented by ChemicalFormula 49 disclosed in Japanese Patent Application No. 163,036/99,titled “Formazan metal complexes” applied for by the same applicant asthe present invention, and the contents were dissolved in the solventwith a 5-minute ultrasonic energization at ambient temperature.Thereafter, in a usual manner, a prescribed volume of the resultingsolution was dropped on either surface of a polished glass substrate, 5cm×5 cm, while the glass substrate was rotated at a rotation rate of1,000 rpm for one minute to uniformly coat the solution thereupon, andsequentially blown with hot air and cold air to dry the coated solution.

The resulting glass substrates coated with the monomethine cyanine dyeswere measured for transmittance (T_(φ)) at the wavelengths of theirabsorption maxima, and then fixed to a position 7 cm apart from a 500 Wxenon lamp and exposed with the light for 25 min while cold air wasblowing to the substrates. Immediately after that, the resultingsubstrates were remeasured for transmittance (T) at the wavelengths ofthe absorption maxima of the monomethine cyanine dyes, and thetransmittances of T and T₀ for each monomethine cyanine dye weresubstituted for the Equation 1 to calculate the residual percentage (%)of each monomethine cyanine dye. In parallel, control systems with nolight-resistant improver for each monomethine cyanine dye were providedand treated similarly as above. The results are shown in Table 2.Equation  1: $\begin{matrix}{{Residual}\quad {percentage}\quad (\%)\quad {of}} \\{{monomethine}\quad {cyanine}\quad {dye}}\end{matrix} = {\frac{100 - T}{100 - T_{0}} \times 100}$

TABLE 2 Residual percentage (%) of monomethine cyanine dye MonomethineWith light-resistant With no light-resistant cyanine dyes improverimprover Chemical Formula 4 100.0 88.6 Chemical Formula 5 100.0 96.6Chemical Formula 6 100.0 98.7 Chemical Formula 17 100.0 80.6 ChemicalFormula 36 93.2 26.0

As shown in the results in Table 2, in the systems with nolight-resistant improver, up to 74% of the monomethine cyanine dye hadchanged with only a 25-min exposure of light to become incapable ofexerting its inherent optical properties. However, in the systems withthe formazan metal complex represented by Chemical Formula 49, all ofthe monomethine cyanine dyes still remained intact up to a level of over93% without changing even after the exposure of light. These resultsindicate that light-resistant improvers such as formazan metal complexesquite effectively inhibit the undesirable changing of the monomethinecyanine dyes inducible by the exposure of light such as natural- andartificial-lights.

EXAMPLE 6 Optical Recording Medium

To TFP was added, as a light absorbent, the monomethine cyanine dye,represented by Formula 6, 14, 16 or 17, to give a concentration of 3.0w/w %, and the mixture was mixed with, as a light-resistant improver,the formazan metal complex represented by Chemical Formula 49 to give aconcentration of 0.35% (w/w), and then heated and energized withultrasound to dissolve the contents. The solution was in a usual mannerfiltered, and the filtrate was coated in a rotary manner over one sideof an acrylic disc substrate, 12 cm in diameter, which concaves forexpressing synchronizing signals and addresses of tracks and sectors hadbeen transferred to the track's internal circuit, and dried to form arecording layer, 200 nm in thickness. Thereafter, the substrate wasspattered with silver to form a reflection layer, 100 nm in thickness,to be closely attached on the surface of the recording layer, and thereflection layer was homogeneously coated in a rotatory manner with“DAICURE CLEAR SD1700”, as a known ultraviolet ray hardening resincommercialized by Dainippon Ink and Chemicals, Inc., Tokyo, Japan, andirradiated to form a protective layer to be closely attached on thesurface of the reflection layer. Thus, four types of optical recordingmedia were obtained.

Every optical recording medium in this example can write a large amountof information in the form of documents, images, and voices at arelatively high density by using laser elements that oscillate atwavelengths of 450 nm or less.

As described above, the present invention was made based on the creationof novel monomethine cyanine dyes and the discovery of theirindustrially useful properties. Since the light absorbents of thepresent invention have absorption maxima in the visible region of arelatively short wavelength and substantially absorb the light in such avisible region, they have a variety of uses in the fields, for example,of optical recording media, optical polymerization, dye lasers, solarbatteries, lithography, and dyeing. Particularly, the monomethinecyanine dyes, which substantially absorb visible light with wavelengthsof 450 nm or less when in a thin layer form, can be advantageouslyuseful as a light absorbent in high-density optical recording media suchas DVD-Rs.

The optical recording media of the present invention, which contain theaforesaid light absorbents and use as a writing light laser beams withwavelengths of 450 nm or less, can form more minute pits on a restrictedrecording surface of the optical recording media at a shorter trackpitch and at a relatively high density, as compared with the DVD-Rs nowavailable which use polymethine dyes as light absorbents and writeinformation using laser beams with wavelengths of 635 nm or 650 nm.Thus, with the optical recording media of the present invention,information in the form of characters, images, and voices, and otherdigital information can be recorded in a single disc of opticalrecording medium at a relatively high density and in a large amount. Asa result, the cost per a bit required for recording information can belowered by a large margin, and moving images and static images can berecorded for a relatively long period of time.

The monomethine cyanine dyes of the present invention with suchusefulness can be easily obtained in a desired yield through a step ofreacting a quaternary ammonium salt of nitrogen-atom-containingheterocyclic compound having a reactive methyl group with a quaternaryammonium salt of nitrogen atom-containing heterocyclic compound havingan appropriate leaving group.

What is claimed is:
 1. A monomethine cyanine dye represented by Formula1;

wherein in Formula 1, when Z is present, Z represents an optionallysubstituted mono or polycyclic aromatic ring or heterocyclic ring whichcondenses to a nitrogen-atom-containing five-membered heterocyclic ring;when Z is not present, substituents which otherwise would have been Zare bound to the positions of Z; A is CCH₂, O, S, and N—R₂, R₁ and R₃are aliphatic hydrocarbon groups and R₂ is a hydrogen atom or the sameor different aliphatic hydrocarbon groups as in R₁ and R₃, wherein thealiphatic hydrocarbon groups are optionally substituted; and X⁻represents an anion.
 2. The monomethine cyanine dye according to claim1, wherein said anion is an organic metal complex anion capable ofimproving light resistance.
 3. The monomethine cyanine dye according toclaim 1, which has an absorption maximum at a wavelength of 450 nm orless.
 4. The monomethine cyanine dye according to claim 1, whichsubstantially absorbs visible light with a wavelength of 450 nm or lesswhen in a thin layer form.
 5. A process for producing any one of themonomethine cyanine dyes according to claim 1, which comprises a step ofeither reacting a compound represented by Formula 9, having R₂ and X⁻corresponding to Formula 1, with a compound represented by Formula 10,having R₃, and X⁻ corresponding to Formula 1; or reacting a compoundrepresented by Formula 11, having R₁, and X⁻ corresponding to Formula 1,with a compound represented by Formula 12, having R₃, and X⁻corresponding to Formula 1,

wherein in Formulae 10 and 11, L represents a leaving group.